1. Field of the Invention
The present invention relates to an apparatus such as a camera which permits loading thereon and use of a film having a magnetic recording part for recording thereon information about the film, information on camera photography, etc., and more particularly to an apparatus arranged to prevent errors in reading magnetically reproduced signals.
2. Description of Related Art
There is known a camera arranged to use a film cartridge which has a film completely contained therein including a leader part, to permit film rewinding (taking out) halfway and to permit reloading and reuse of a film cartridge taken out, as disclosed in U.S. Pat. No. 4,878,057. Further, a film cartridge arranged to indicate its state, such as an unused state, a currently-in-use state or a used state, was proposed in U.S. Pat. No. 4,965,600. In addition, the art of providing a magnetic recording part on a film and reproducing and recording information on the film or information on camera photography was disclosed in U.S. Pat. No. 4,864,332.
A camera using a film of the above-stated kind is arranged to detect exposure information from a visual exposure indication (VEI) provided on the film cartridge and also from magnetic information recorded on the film. By virtue of this arrangement, a photo-taking operation can be resumed on a film which has been rewound halfway in use, by loading the film again on the camera and setting an unexposed (unused) portion of the film on the camera.
A camera of the above-stated kind is arranged to discriminate between an exposed frame and an unexposed frame in a film in which magnetic information has been recorded on the exposed frames, by detecting the magnetic information recorded on the film, in setting an unexposed portion of the film with the film reloaded on the camera after the film has been rewound halfway in use. In the case of the camera of this kind, a spike-like magnetic noise caused by a film transport motor while the camera is in process of detecting the magnetic information from the film tends to prevent the magnetic information from being accurately detected. The spike-like magnetic noise thus has presented a serious problem.
To solve this problem, there has been proposed in Japanese Laid-Open Patent Application No. HEI 4-246638 an arrangement for canceling the spike-like magnetic noise by using a delay circuit for a signal obtained by binary-coding an analog magnetic signal. However, when the level of noise other than the spike-like motor magnetic noise is large or the level of magnetic information itself is small, such proposed arrangement not only makes it difficult to set a comparison voltage for a comparator to be used in binary-coding the analog signal but also tends to make discrimination between an unexposed frame and an exposed frame difficult as the magnetic information cannot be accurately detected.
If a camera is required to simply discriminate between an exposed frame and an unexposed frame, the camera can be arranged to detect the presence or absence of a magnetic record instead of reading the contents of information recorded. In that case, an analog signal value of a magnetic information signal is continuously A/D (analog-to-digital) converted for a predetermined period for each of frames to obtain a standard deviation of a plurality of A/D-converted values, and the value of the obtained standard deviation is compared with a prestored standard deviation of A/D-converted values of a frame in which no magnetic information is recorded. Then, each frame is checked to find if magnetic information is recorded for the frame according to the result of the comparison. If so, the frame is determined to be an exposed frame. An unexposed frame thus can be detected by utilizing the fact that the level of a signal differs between the frame in which magnetic information is recorded and the frame in which no magnetic information is recorded.
The above-stated prior art arrangement employs a method of obtaining the standard deviation of A/D converted values. However, although unexposed frames can be found or indexed at a fairly high probability by the above-stated method, the spike-like magnetic noise caused by the film transport motor is also necessarily A/D-converted. Therefore, according to the above-stated method, it is hardly possible to completely remove the adverse effect of the spike-like magnetic noise. Then, depending on the degree of the adverse effect of the spike-like magnetic noise, the magnetic noise might cause the exposed state of the film in use to be erroneously detected, such that an unexposed frame is mistaken for an exposed frame, thereby making an accurate indexing action for unexposed frames hardly possible.
Further, the adverse effect of the motor noise mentioned above can be mitigated by arranging the motor away from a magnetic head. However, a strong desire which generally exists for reduction in size of a camera imposes a limit on a physically allowable space between the magnetic head and the motor. Therefore, the noise in question cannot be sufficiently mitigated.